If I understand Jacques’ explanation correctly: It had been on by default, always had been. But up until the issue I filed it was not possible to turn off this build in ciecam artefact safety net.
Now you can turn it off, but it should only be used in those rare situations that everything aligns (in)correctly. If you leave it off you might run into other, more common artefact problems (@jdc: please correct me if I’m wrong…)
Jacues did elaborate a bit more about the inner workings of this very old problem and its solution in the above mentioned/linked PR and issue.